When Yesterday's Number Doesn't Match Today's: Measuring Under the Same Conditions

"It Was 42 Yesterday, Now It's 38"

Every team that starts measuring runs into this question after two or three weeks. An athlete who jumped 42 cm last week gets 38 cm today. Is the athlete in worse shape, or did the measurement go wrong?

If you can't answer that, the data loses its power. Coaches start waving off drops with "must have been an off day" and shrugging off gains with "got lucky." At that point you can measure all you want and training never changes.

To trust a number, you first have to know how much it moves on its own. If a 4 cm swing is normal for this athlete, it's noise, not signal. If that same athlete usually stays within 1 cm, then 4 cm is a real change. Making that distinction doesn't take statistics — it takes measurement habits.

At a Glance Numbers usually move because of measurement conditions, not the device Locking down sensor placement, time of day, order, warm-up, and movement pattern cuts the swing sharply Take several attempts and check the coefficient of variation (CV) to know whether today's session is trustworthy Judge on the trend, not a single value, and compare each athlete against their own baseline Build measurements into a program and assign it, so the procedure survives a change of coach

Most of the Swing Comes From Conditions

The human body changes within a single day. Morning differs from evening, before training differs from after, and last night's sleep shifts things again. That part is outside a coach's control.

The problem is when measurement conditions change on top of that. If you measured before training last week and after training this week, if the warm-up was thorough last time and skipped this time, and if the sensor sat in a slightly different spot, then pulling the fitness change out of that number gets hard.

The second half is what a coach controls. Fix the conditions and whatever difference remains sits much closer to the athlete's actual change. Settling these five items solves most of it.

Condition 1. Same Spot, Firmly Attached

Accurate measurement starts with a sensor that doesn't wobble or slide. A loose mount mixes the sensor's own movement into the athlete's. Tighten the strap to the same degree every time.

Placement differs by measurement. For jump and reactive strength index (RSI), strap the sensor to the top of the shoe. Single-leg variants sit in the same place — just on the jumping foot. For 1RM and weightlifting, mount it on the barbell. Velocity based training (VBT) depends on the exercise: barbell work on the bar, dumbbells and kettlebells on the wrist, bodyweight work on the torso, cables and machines on the weight stack. Swing and throws go on the wrist, and isometrics sit on the torso or thigh depending on the position. Both the app and the web show the placement for whichever measurement you select, so check there when in doubt.

The mistake teams make most often is changing placement within the same measurement. Say you move the sensor to the wrist to protect it during a lift where the bar gets dropped — the app even notes that accuracy may drop somewhat in that case. Change it if you have to, but keep that athlete's version of that measurement on the same spot from then on. Don't line up last month's barbell records against this month's wrist records and conclude the athlete got slower.

The same goes for rotation measurements. The farther the sensor sits from the center of rotation, the higher the linear velocity reads. To compare an athlete across two months, keep the mounting point exactly where you first set it.

Condition 2. Fix the Time and the Order

A jump measured before training and a jump measured after training are not the same metric. Both mean something, but they can't be mixed. Set a team rule like "jump and RSI on Tuesday before training starts" or "velocity based training during working sets."

Order matters too. Measure maximal strength first and the jump that follows will come out low. When you run several measurements in one session, lock in an order that puts power-focused work up front and fatiguing work at the back.

Matching the day of the week helps as well. Monday reads well after a weekend of rest, Thursday reads low with midweek training stacked up — that's normal. Alternating between the two manufactures swings that were never there.

Condition 3. Same Warm-Up Every Time

The warm-up right before measurement changes the result a lot, and measurements that rely on instant force output — jump and RSI especially — are sensitive to how prepared the athlete is. "Loosen up a bit and go" means different things to different people.

So write the warm-up down as a sentence: which movements, how many reps, how many minutes, how long a rest before measuring. This matters even more with several coaches on staff. If coach A's warm-up differs from coach B's, an athlete's numbers start depending on who ran the session.

Condition 4. Same Movement Pattern

Even within "jump," using a countermovement, swinging the arms, or dipping to a different depth produces different numbers. That's why the app and the web separate countermovement jump, squat jump, Abalakov (arm-swing jump), and depth jump into distinct types and show on screen how each one is performed. Reactive strength index splits into continuous jump, drop jump, and single-leg jump as well. Pick the same type every time so athletes don't mix them.

Measurements with settings — like jumps that start from a box — need those values fixed too. If box height goes from 30 cm to 40 cm, contact time changes and so does RSI. The same applies to measurements where you enter body weight or medicine ball weight: change the value and the result means something else.

If the movement is too small, it may not register as a rep at all. When reps go missing, first check whether the athlete is using the full range of motion and whether the sensor is still firmly in place.

Condition 5. Keep the Sensor in Shape

Sensors need calibration for accurate measurement. Fortunately there's nothing for a coach to calculate. The app and the web tell you when it's time, and you just follow the on-screen instructions. Gyroscope calibration means resting the sensor still on a flat surface; accelerometer calibration means turning the sensor face by face as prompted.

Jump measurement includes a step where the athlete stands still during a countdown. Movement there shifts the reference, so tell athletes to hold still until the count ends. Mobility measurement sets a zero point from a reference posture on the goniometer screen, and that reference posture also has to be the same every time for left–right and trend comparisons to hold.

Calibration prompts appear based on the sensor's state — when a while has passed since the last calibration, when the temperature has shifted noticeably, or when values are detected drifting after a set. Don't dismiss the prompt; handle it on the spot. The next set comes back steadier.

Put a Number on the Swing

Even with every condition matched, values still move somewhat. What matters is knowing the size of that movement.

The easiest approach is not to measure only once. For measurements with multiple attempts — jump, RSI, throws — run three to five and look at how spread out the attempts are. PoinT GO calculates this automatically as the coefficient of variation (CV) and shows it on the result screen. It expresses how far individual attempts sat from the average, as a percentage, and lower means the session was more stable. The screen displays it with color and a grade, so you read it directly without doing any math.

You can use this number two ways.

First, to judge whether to trust that day's data. If the spread across attempts came out wide, the best value from that day is weak evidence. Recheck the conditions and measure again. Usually the sensor was loose, the warm-up was short, or the athlete performed the movement differently each time.

Second, to treat consistency itself as a metric. An athlete whose attempts stay widely spread even with conditions matched hasn't stabilized the movement yet. You can't see that by looking at the best value alone — but competition performance lands closer to the average, so there's something to address in training.

Telling Real Change From Measurement Noise

Back to the original question. Is the drop from 42 cm to 38 cm meaningful?

As a rule, don't decide from a single measurement. Look at three things together.

What to check	How to check it	Verdict
Was the session stable	Spread across attempts (CV)	Wide spread — set the day's value aside
What's this athlete's normal range	Record range over recent weeks	Inside the usual range — closer to noise
Does the direction hold	Trend chart	Same direction two or three times running — real change

The key is that the baseline differs by athlete. One athlete swings 3–4 cm routinely; another stays within 1 cm. The comparison has to be against that athlete's own record range, not the team average or somebody else's numbers. That's why repeated measurement over the first few weeks of a season — building each athlete's baseline and normal swing — matters so much.

The web dashboard charts each athlete's trend, so whether today's value falls inside or outside their usual range is immediately visible. Reading the line instead of a single point makes the judgment accurate.

Write Your Team Protocol on One Page

Turning all of this into team rules looks like the table below. Write one line per measurement type and post it on the wall or share it as a team document.

Item	What to decide
Measurement type	One exact type — countermovement jump, continuous jump, etc.
Sensor placement	Mounting point and strap type
Timing	Day, time of day, before or after training
Order	Sequence when running several measurements
Warm-up	Movements, reps, and rest time
Settings	Box height, target reps, body weight and load inputs
Attempts	How many, and what gets recorded

Once set, it's best not to change it during the season. If you do have to change the protocol, note the date. You can't compare records across that line as if they were continuous.

Making the Protocol Stick

Rules kept only in people's heads eventually drift, and that gets worse with several coaches or more than twenty athletes.

In PoinT GO you can build a measurement setup into a training program and assign it to athletes. Put the measurements and their settings into the program — box height and target reps included — and sessions run as assigned instead of being configured from scratch each time. The procedure stays the same even when the coach in charge changes.

It also matters that the tool doesn't shift the standard. Field sessions happen in the app while the office reviews things on the web, and PoinT GO shares the same measurement algorithms across both. Which side you measured on doesn't change the basis of the metrics. Measured data syncs in real time, so you can carry on with team-wide trends and athlete comparisons on the web.

The calculations behind the numbers are handled automatically by PoinT GO's proprietary algorithms, built on optimized 9-axis IMU technology. What a coach needs to worry about is keeping the conditions consistent — that's where it ends.

Try This Today

Pick the measurement your team runs most often. Write its sensor placement, timing, order, warm-up, and settings on a single page, and follow it exactly from the next session on. Then run at least three attempts and see how big the spread is.

Collect that for two or three weeks and each athlete develops a boundary between "a difference that's always there" and "something that actually changed." From the moment that boundary exists, your measurements start changing training.